Fix clang reject valid C++ code after d999ce0 (#94471)

The incremental processing mode doesn't seem to work well for C++, see
the
#89804 (comment)
for details.

Author: hokein

clang/lib/Interpreter/IncrementalParser.cpp

@@ -413,7 +413,8 @@ void IncrementalParser::CleanUpPTU(PartialTranslationUnit &PTU) {
     if (!ND)
       continue;
     // Check if we need to clean up the IdResolver chain.
-    if (ND->getDeclName().getFETokenInfo())
+    if (ND->getDeclName().getFETokenInfo() && !D->getLangOpts().ObjC &&
+        !D->getLangOpts().CPlusPlus)
       getCI()->getSema().IdResolver.RemoveDecl(ND);
   }
 }

clang/lib/Sema/SemaDecl.cpp

@@ -2288,7 +2288,8 @@ void Sema::ActOnPopScope(SourceLocation Loc, Scope *S) {
     // Partial translation units that are created in incremental processing must
     // not clean up the IdResolver because PTUs should take into account the
     // declarations that came from previous PTUs.
-    if (!PP.isIncrementalProcessingEnabled() || getLangOpts().ObjC)
+    if (!PP.isIncrementalProcessingEnabled() || getLangOpts().ObjC ||
+        getLangOpts().CPlusPlus)
       IdResolver.RemoveDecl(D);
 
     // Warn on it if we are shadowing a declaration.